Lead-calcium alloys, particularly for battery grids

ABSTRACT

A lead alloy for battery grids is disclosed. The lead alloy contains calcium with a relative concentration by weight of between 0.05% and 0.12%; tin with a relative concentration by weight of less than 3%; aluminum with a relative concentration by weight of between 0.002% and 0.04%; and barium comprising a relative concentration by weight of less than 0.02%.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to lead-calcium-aluminum alloys usedmainly in the manufacture of lead-acid battery grids of which so-called“maintenance-free” start-up batteries are composed.

2. Background Information

For some twenty years, the substitution of antimony with calcium andwith tin in the lead making up these grids has led to a growing numberof storage batteries of longer life and having a negligible consumptionof electrolyte being put on the automobile market.

This is because calcium gives lead very useful mechanical properties andtin, while also hardening the lead, favors better energy transfer duringthe repeated charging/discharging cycles that the battery undergoesthroughout its life.

Lead-calcium (Pb—Ca) and lead-calcium-tin (Pb—Ca—Sn) alloy manufacturersalso add a small amount of aluminum intended to protect the baths forproducing the alloy from extensive oxidation, which consumes mostlycalcium at the expense of lead.

Lead-calcium-aluminum (Pb—Ca—Al) alloys, with or without tin, are usedfor manufacturing negative grids for batteries, whilelead-calcium-aluminum-tin (Pb—Ca—Al—Sn) alloys are used formanufacturing positive grids.

The manufacture of a storage battery is a succession of a large numberof operations, some of which are carried out between 60 and 80° C. overperiods ranging from twenty-four to forty-eight hours. These operationsallow the alloy and the active substance to be given all the propertieswhich they will subsequently have to have in order for the battery tooperate correctly.

The development of new continuous processes for manufacturing batterygrids has, moreover, given rise to a recent requirement for newmaterials meeting the specifications of new casting and expandingmachines and allowing the production of positive or negative grids ofhigh quality.

In the case of negative grids, the tendency is to developlead-calcium-aluminum alloys having low contents of tin which rapidlyhardens over time, thereby making it possible to increase theproductivity of casting machines. They must furthermore have mechanicalproperties superior to those of the previous generation, so as to allowa reduction in the thickness of the grid and therefore a reduction inthe weight of the battery without concomitantly impairing the mechanicalintegrity of the negative plate.

In the case of positive grids, the tendency is to developlead-calcium-aluminum-tin alloys resistant to the corrosion andpassivation phenomena which occur in the positive plate. They must alsohave a sufficiently high hardness or tensile strength so as towithstand, throughout the lifetime of the battery, the mechanicalstresses which are exerted in the positive plate.

In point of fact, the manufacture of positive and negative battery gridsrequires special attention during the first step of pasting. During thisoperation, the freshly cast grid must in fact be sufficiently rigid notto deform under the pressure of applying the lead oxide paste which willfill the grid. Since the family of lead-calcium-aluminum-tin alloys isknown for its room-temperature hardening properties, the rapidity of thekinetics of which process may vary, the battery manufacturer's know-howand that of his supplier are constantly being applied in order tooptimize the efficiency and the quality of the manufacture. One methodconsists in providing temporary storage of the grids (individual gridsor a set of rolls) so as to allow the hardening phenomenon time todevelop. The use of a lead alloy having rapid hardening kinetics shouldallow the time for storing the grids to be reduced.

However, deformation, or even final fracture, of grids during their usein a battery remains one of the main quality problems with which batterymanufacturers are confronted. This problem, which is particularlysensitive in the case of positive grids subjected to high mechanical andchemical stresses (corrosion in a sulfuric medium) requires thedevelopment of alloys which exhibit good corrosion resistance in asulfuric medium and have mechanical properties which are high and remainconstant over time.

However, it is recognized that one of the simplest means of reducing thesensitivity of thin battery grids to grain-boundary corrosion is to use,in their manufacture, alloys which solidify in a crystallographicstructure containing small grains, since this type of structure isreputed to be less sensitive to grain-boundary corrosion.

In order to solve these problems, the addition of barium inlead-calcium-tin alloys has already formed the subject of prior studiesmentioned, for example, in Patents FR-A-851,686, DE-2,611,575,DE-2,619,113, EP-A-040,951, DE-2,921,290, GB-1,597,270 and GB-1,304,095.However, although it is actually mentioned that the presence of bariumsubstantially improves the mechanical integrity of cast grids(mechanical strength and creep strength) while not degrading theircorrosion behavior, the relative barium contents by weight proposed arealways greater than 0.025%. For example, from 0.05 to 0.5% barium isfound in the case of DE-2,619,113 and DE-2,611,575; from 0.026 to 0.044%as a complete calcium substitute is found in the case of GB-1,597,270and DE-2,921,290; and from 0.025 to 0.1% barium with, systematically,strontium between 0.15 and 0.4% and a calcium content of from 0.03 to0.04% are found in the case of EP-A-040,951 and/or are combined withother additions (magnesium and lithium).

Incidentally, it may be pointed out that Patent FR-A-851,686 recommendsan alloy having very high barium contents for producing railroadbearings. For example, it refers to a lead-calcium-barium alloycontaining from 0.1% to 2% calcium, from 0.5% to 10% tin and from 0.02%to 0.1% barium. This patent mentions that this alloy has very goodcorrosion resistance properties in organic medium (oils).

The only reference to alloys having low barium contents is found inGB-1,304,095 which mentions, generally, the beneficial effects of addingfrom 0.001 to 1% barium, but in an alloy not containing calcium.

An exhaustive study of the prior documents shows that most of thestudies carried out in the past related to alloys with or withoutcalcium and having high barium contents (greater than 0.02%).

SUMMARY OF THE INVENTION

The Applicant has discovered, surprisingly and unexpectedly, that, bydecreasing the barium content, the properties of these alloys wereradically improved compared with the known alloys, especially withregard to their speed of hardening, their high hardness and theirability to retain mechanical properties which are constant over time.

The present invention thus provides novel alloys of the aforementionedtype, in which the relative barium concentration by weight is less than0.02%.

More specifically, the present invention thus provides a lead alloy forlead-acid battery grids containing calcium, with a relativeconcentration by weight of between 0.05% and 0.12%, tin, with a relativeconcentration by weight of less than 3%, aluminum, with a relativeconcentration by weight of between 0.002% and 0.04% and barium,characterized in that the relative concentration by weight of barium isless than 0.02%.

A lead alloy according to the invention, having a relative concentrationby weight of tin of less than 0.75% and a relative concentration byweight of barium of between 0.0015% and 0.015%, so as to obtain rapidlyhardening alloy, is preferably intended for negative grids.

The role of the barium in this family of alloys is to appreciably speedup the hardening kinetics immediately after casting and to substantiallyincrease the maximum hardness of the alloy.

A lead alloy according to the invention, having a relative concentrationby weight of tin of between 0.75% and 1.5% and a relative concentrationby weight of barium of between 0.0015% and 0.02% is preferably intendedfor positive grids.

Advantageously, the relative concentration by weight of calcium isbetween 0.06 and 0.085% and the relative concentration by weight of tinis between 0.9 and 1.4%.

The addition of barium to this second family of alloys allows the metalto retain high mechanical properties throughout the lifetime of thebattery and is conducive, during solidification, to the formation of afine crystalline structure.

According to the invention, the alloy may furthermore contain bismuthwith a relative concentration by weight of between 0.001% and 0.025% orelse silver with a relative concentration by weight of less than 0.005%and preferably of between 0.0005% and 0.005%.

The presence of bismuth or silver is not troublesome and has no effecton the hardness of the alloy.

The invention also relates to the lead-acid battery grids comprising apart made of a lead alloy described above, as well as to the lead-acidbatteries comprising at least one of these grids.

The following description, with reference to the figures and to theexamples appended hereto, which compare the properties of the same alloywith and without barium doping, will make it easier to understand howthe invention may be realized. These examples illustrate the excellentproperties of PbCaSnAl alloys containing small amounts of barium asopposed to the same alloys without barium.

BRIEF DESCRIPTION OF THE DRAWINGS

Other aspects, objects and advantages of the present invention willbecome clearer on reading the following detailed description, given withreference to the appended drawings, in which:

FIG. 1 illustrates the variation in the Vickers hardness as a functionof time, at 20° C., in the case of PbCaAl alloys which contain 0.056%and 0.099% calcium and are doped with 0.004% barium or undoped;

FIG. 2 illustrates the variation in the Vickers hardness as a functionof time, at 20° C., in the case of PbCaAl alloys which contain 0.0566and 0.0996 calcium and are doped with 0.007% barium or undoped;

FIG. 3 illustrates the variation in the Vickers hardness as a functionof time, at 20° C., in the case of PbCaAl alloys which contain 0.056%and 0.099% calcium and are doped with 0.013% barium or undoped;

FIG. 4 illustrates the variation in the Vickers hardness as a functionof time, at 60° C., in the case of PbCaSnAl alloys which contain 0.06%calcium and 1.2% tin and are doped with 0.008% barium or undoped;

FIG. 5 illustrates the variation in the Vickers hardness as a functionof time, at 60° C., in the case of PbCaSnAl alloys which contain 0.075%calcium, 1.2% tin and are doped with 0.008% barium or undoped;

FIG. 6 illustrates the variation in the Vickers hardness as a functionof time, at 60° C., in the case of PbCaSnAl alloys which contain 0.085%calcium, 1.2% tin and are doped with 0.008% and 0.016% barium orundoped.

FIG. 7 illustrates the microstructures of 0.75% Ca/1.2% Sn/0.008% Al/Pballoys doped with 0.0.16% barium immediately after casting.

FIG. 8 illustrates the microstructures of 0.75% Ca/1.2% Sn/0.008% Al/Pballoys (undoped) immediately after casting.

FIG. 9 illustrates the microstructures of the polished sections removedfrom an alloy plate.

FIG. 10 illustrates the microstructures of the polished sections removedfrom an alloy plate.

DERAILED DESCRIPTION OF THE INVENTION EXAMPLES

Alloys of the PbCaAl and PbCaSnAl family, optionally doped with barium,are prepared. The Vickers hardness of these alloys is measured as afunction of the barium concentration. Finally, these hardnessmeasurements are compared in the case of a family of alloys according tothe barium concentration.

The alloys are produced in the following manner:

Commercial second-melting alloys are used as the base alloy. Therelative composition by weight of these alloys is given in Tables I andII. So-called soft (first-melting) lead is added. Its composition isgiven in Table III. Also added are 19% Sn/Pb, 0.4% Ba/Pb and 0.14%Ca/0.13% Ba/Pb master alloys, depending on the case.

In all the tables, the compositions are expressed in relativepercentages by weight.

All these components are mixed at a temperature of between 550 and 600°C. in air until casting.

The alloys are cast in the form of 130 mm×70 mm×3 mm plates in a coppermold, the initial temperature of which is room temperature.

Chemical analysis of these plates, especially barium analysis, wassystematically checked using spark spectroscopy calibrated by Pb—Baalloys having very low barium contents.

For each composition, the variation in the Vickers hardness aftersolidification is measured over a so-called aging period. This agingtakes place at 20° C., over periods ranging from 0 to 6600 hours (h), inthe case of rapidly hardening alloys and at 60° C., over periods rangingfrom 0 to 400 h, in the case of alloys intended for the production ofpositive grids. The 20° C. aging phases simulate the phases during whichthe grids are cooled and stored after casting but before pasting. The60° C. aging phases reproduce industrial pasting, ripening and formingconditions and allow artificial simulation of the phenomena which occurin positive plates during the lifetime of a battery.

The results obtained on the rapidly hardening alloys are given in TablesIV to VII below. All the percentages expressed in these tables are alsorelative percentages by weight, while the Vickers hardness, expressed inHv2 units, was measured for a 2 kg load.

Table IV gives the Vickers hardnesses (Hv2) of the 0.065% Ca/0.008%Al/Pb alloy variously doped with barium, for different aging times at20° C.

Table V gives the Vickers hardnesses (Hv2) of the 0,099% Ca/0.008% Al/Pballoy variously doped with barium, for different aging times at 20° C.

Table VI gives the Vickers hardnesses (Hv2) of the 0.099% Ca/0.6%Sn/0.008% Al/Pb alloy variously doped with barium, for different agingtimes at 20° C.

Table VII gives the Vickers hardnesses (Hv2) of various x % Ca/0.008%Al/Pb alloys, with various calcium contents (x), doped with 0.015%barium or undoped, after 288 h or 6600 h at 20° C.

For each of Tables IV, V, VI and VII, it may be noticed that:

the hardness of the alloys is always higher in the presence of barium(between 0.002% and 0.02%) than in the absence of barium;

the hardness of the alloys may reach 20 Hv2 in the presence of barium;

the hardness always increases more rapidly with aging time at 20° C. inthe presence of barium (between 0.002% and 0.015%) than in the absenceof barium;

the alloys doped with barium retain very high hardnesses even afterparticularly long aging times (6600 h, i.e. 275 days).

These tables illustrate the excellent properties of the PbCaSnAl alloysaccording to the invention in terms of hardness and hardening rate.

FIGS. 1 to 3 show the variation in the Vickers hardness as a function oftime for two PbCaSnAl alloys in the case in which the alloy is dopedwith barium or undoped.

In each of these figures, the symbols when open correspond to undopedalloys and when solid correspond to doped alloys.

In FIGS. 1 to 3, it is clear that when the alloys are in accordance withthe characteristics of the present invention, the addition of smallamounts of Ba makes it possible:

to increase the initial hardness of the alloy,

to increase the maximum hardness of the alloy,

to speed up the hardening kinetics of the alloy.

It follows that the addition of barium to the PbCaSnAl alloys accordingto the invention has the effect both of increasing the initial andmaximum hardnesses of the alloys intended for the production of batterygrids and of speeding up the hardening kinetics of the alloys, therebymaking it possible to reach the minimum hardness necessary for thepasting operation more rapidly.

The results obtained on the alloys intended for the production ofpositive grids are given in Tables VIII to XI below. All the percentagesexpressed in the tables are percentages by weight. The Vickers hardness,expressed in Hv2 units, was measured for a 2 kg load while the tensiletests were carried out with a pull rate of 10 mm/min.

Table VIII gives the Vickers hardnesses (Hv2) of the 0.06% Ca/1.2%Sn/0.008% Al/Pb alloy variously doped with barium, for different agingtimes at 60° C.

Table IX gives the Vickers hardnesses (Hv2) of the 0.075% Ca/1.2%Sn/0.008% Al/Pb alloy variously doped with barium, for different agingtimes at 60° C.

Table X gives the Vickers hardnesses (Hv2) of the 0.085% Ca/1.2%Sn/0.008% Al/Pb alloy variously doped with barium, for different agingtimes at 60° C.

Table XI gives the tensile strength R_(m) (MPa) measured in tensiletests on specimens of the 0.075% Ca/1.2% Sn/0.008% Al/Pb alloy variouslydoped with barium, for different aging times at 60° C.

Again for all these tables, the concentrations are relativeconcentrations by weight.

It may be noted in Tables VIII, IX, X and XI that:

the hardness of the alloys, immediately after casting, is higher in thepresence of barium (between 0.002% and 0.018%) than in the absence ofbarium;

the hardness of the alloys goes through a maximum and then decreases inthe absence of barium, but increases and remains stable at a high levelin the presence of barium;

the tensile strength of the alloys goes through a maximum and thendecreases in the absence of barium, but increases and remains stable ata high level in the presence of barium;

the maximum hardness may reach 23 Hv2 in the presence of barium;

the tensile strength may reach 60 MPa in the presence of barium.

These tables illustrate the excellent properties of the PbCaSnAl alloysin terms of hardness, tensile strength, hardening rate and stabilityover time when their concentrations are in accordance with thecharacteristics of the present invention.

Each of FIGS. 4 to 6 shows, in the case of a PbCaSnAl alloy, thevariation in the Vickers hardness as a function of time depending onwhether or not the alloy is doped with Ba.

In each of these figures, the symbols, when open, correspond to undopedalloys and when solid correspond to doped alloys.

It is apparent in FIGS. 4 to 6, that, when the alloys are in accordancewith the invention, the addition of small amounts of barium makes itpossible:

to increase the initial hardness of the alloy at the time t=0;

to stabilize, over time, the hardness and the tensile strength of thealloy to a high value.

Photographs such as those shown in FIGS. 7 through 10 show themicrostructures of 0.075% Ca/1.2% Sn/0.008% Al/Pb alloys, doped with0.016% barium or undoped, immediately after casting (FIGS. 7 and 8) andafter an aging time of 270 h at 60° C. (FIGS. 9 and 10). These photoswere taken on polished sections removed from the same alloy plate castat 600° C. in a 3 mm thick copper mold.

In each of these photos, the black band at the top of the photocorresponds to the end of the plate in contact with the mold.

By comparing the photographs shown in FIG. 7 with FIG. 8 and FIG. 9 withFIG. 10, it is clear that, when the alloys are in accordance with thecharacteristics of the present invention, the addition of small amountsof barium makes it possible:

to transform the coarse-grained cast structure characteristic of thistype of alloy into a finer-grained structure (Photos 1 and 2);

to eliminate the so-called averaging or lamellar-precipitationphenomenon within the grains, this being clearly visible in the alloysnot containing barium (Photos 3 and 4);

to promote the formation of a finer-grained crystallographic structurewhich remains stable over time (FIGS. 9 and 10).

It follows that the alloys according to the invention contain an amountof barium which has the effect both of increasing the initial hardnessof the alloy and of making the PbCaSnAl alloy less sensitive to theaveraging phenomena which are manifested by a transformation of thecrystallographic structure of the alloy and by a drop in mechanicalproperties of the alloy over time.

Although the Applicant does not have at the present time a completetheoretical explanation and does not favor any one argument, it may bestated that the excellent results obtained on the PbCaSnAl alloysappear, in the case of barium contents, below the solubility limit insoft lead. It is therefore possible that a synergy exists betweencalcium and barium, the latter, possibly, being better able to help indistributing the calcium supersaturation in the plumbiferous matrix,thereby improving the hardening process of the alloy. This synergy wouldonly appear when the barium is in solid solution, i.e. when its contentis less than the solubility limit, i.e., according to J. L. Dawson (“TheElectrochemistry of Lead”, Ed. Kuhn, Academic Press, 1979, p. 309),0.02% at 25° C. in soft lead.

TABLE I Composition of one of the commercial base alloys Minimum MaximumElement content content Silver — 0.0050 Ag (%) Bismuth — 0.0300 Bi (%)Arsenic — 0.0020 As (%) Cadmium — 0.0010 Cd (%) Copper — 0.0050 Cu (%)Nickel — 0.0020 Ni (%) Antimony — 0.0010 Sb (%) Tin — 0.0500 Sn (%) Zinc— 0.0010 Zn (%) Tellurium — 0.0010 Te (%) Selenium — Se (%) Sulfur — S(%) Calcium 0.1000 0.1400 Ca (%) Aluminum 0.0150 0.0250 Al (%) Sodium —Na (%) Magnesium — Mg (%) Iron — 0.0050 Fe (%) Cobalt — Co (%)

TABLE II Composition of one of the commercial base alloys MinimumMaximum Element content content Silver — 0.0040 Ag (%) Bismuth — 0.0180Bi (%) Arsenic — 0.0030 As (%) Cadmium — 0.0010 Cd (%) Copper — 0.0005Cu (%) Nickel — 0.0020 Ni (%) Antimony — 0.0010 Sb (%) Tin 0.5500 0.6500Sn (%) Zinc — 0.010 Zn (%) Tellurium — 0.0010 Te (%) Selenium — Se (%)Sulfur — S (%) Calcium 0.1000 0.1200 Ca (%) Aluminum 0.0100 0.0200 Al(%) Sodium — Na (%) Magnesium — Mg (%) Iron — 0.0005 Fe (%) Cobalt — Co(%)

TABLE III Composition of the so-called first-melting soft lead MinimumMaximum Element content content Silver — 0.0010 Ag (%) Bismuth — 0.0100Bi (%) Arsenic — 0.0001 As (%) Cadmium — 0.0003 Cd (%) Antimony — 0.0003Sb (%) Tin — 0.0003 Sn (%) Zinc — 0.0010 Zn (%) Copper — 0.0010 Cu (%)Iron — 0.0010 Fe (%)

TABLE IV 0.065% Ca/0% Sn/0.008% Al/Pb Hv2 (aging at 20° C.) Time (h) Ba= 0% Ba = 0.0015% Ba = 0.004% Ba = 0.007% 0.25 11.7 — 11.5 10.5 2.5 12.315.4 15.2 16.0 23 13.7 15.9 18.7 16.6 45 14.8 16.7 18.3 17.9

TABLE IV 0.065% Ca/0% Sn/0.008% Al/Pb Hv2 (aging at 20° C.) Time (h) Ba= 0% Ba = 0.0015% Ba = 0.004% Ba = 0.007% 0.25 11.7 — 11.5 10.5 2.5 12.315.4 15.2 16.0 23 13.7 15.9 18.7 16.6 45 14.8 16.7 18.3 17.9

TABLE VI 0.0990% Ca/0.6% Sn/0.0080% Al/Pb Hv2 (aging at 20° C.) Time (h)Ba = 0% Ba = 0.003% Ba = 0.006% Ba = 0.02% 0.25 13.3 17.6 17.7 12.5 514.4 17.3 18.1 12.2 24 15.4 17.2 18.5 — 48 16.0 18.4 18.5 — 75 — — —15.7 250 18.0 19.2 21.0 17.8 1000 — 21.5 22.6 —

TABLE VI 0.0990% Ca/0.6% Sn/0.0080% Al/Pb Hv2 (aging at 20° C.) Time (h)Ba = 0% Ba = 0.003% Ba = 0.006% Ba = 0.02% 0.25 13.3 17.6 17.7 12.5 514.4 17.3 18.1 12.2 24 15.4 17.2 18.5 — 48 16.0 18.4 18.5 — 75 — — —15.7 250 18.0 19.2 21.0 17.8 1000 — 21.5 22.6 —

TABLE VIII 0.06% Ca/1.2% Sn/0.008% Al/Pb Hv2 (aging at 60° C.) Time (h)Ba = 0% Ba = 0.004% Ba = 0.008% Ba = 0.015% 0 7.4 8.6 7.8 8.8 24 17.716.3 17.6 17.7 48 18.5 18.7 18.7 17.9 72 20.4 20.2 20.2 20.0 96 19.820.0 19.6 20.5 168 20.3 21.3 21.2 20.2 264 18.2 20.2 23.2 21.9 336 17.521.0 22.5 22.3 504 17.0 21.6 23.0 23.6

TABLE VIII 0.06% Ca/1.2% Sn/0.008% Al/Pb Hv2 (aging at 60° C.) Time (h)Ba = 0% Ba = 0.004% Ba = 0.008% Ba = 0.015% 0 7.4 8.6 7.8 8.8 24 17.716.3 17.6 17.7 48 18.5 18.7 18.7 17.9 72 20.4 20.2 20.2 20.0 96 19.820.0 19.6 20.5 168 20.3 21.3 21.2 20.2 264 18.2 20.2 23.2 21.9 336 17.521.0 22.5 22.3 504 17.0 21.6 23.0 23.6

TABLE X 0.0850% Ca/1.2% Sn/0.0080% Al/Pb Time Hv2 (aging at 60° C.) (h)Ba = 0% Ba = 0.0040% Ba = 0.0080% Ba = 0.0160% 0 8.7 9.2 10.4 11.2 2417.2 17.7 17.7 16.9 48 19.0 18.6 18.7 18.5 72 18.7 18.6 19.5 19.2 9617.3 17.9 19.8 19.4 168 17.3 18.2 20.6 20.7 264 17.0 17.2 19.1 22.8 33616.7 16.9 18.1 21.6 504 17.1 16.6 17.7 22.5

TABLE XI 0.0750% Ca/1.2% Sn/Pb Mechanical properties of alloys forpositives Ba (%) R_(m) R_(m) R_(m) Time, Hv2 (−) (MPa) Hv2 (−) (MPa) Hv2(−) (MPa) Temper- 0h at 0h at 72h at 72h at 290h at 290h at ature 60° C.60° C. 60° C. 60° C. 60° C. 60° C. 0 8.3 20.0 20.4 50.3 16.3 40.7 0.00378.8 22.3 19.9 50.0 18.6 51.3 0.0086 9.9 20.0 19.6 49.7 22.6 56.0 0.016610.7 22.7 19.7 50.0 23.2 60.0

What is claimed is:
 1. Lead alloy for lead-acid battery grids consistingessentially of calcium having a concentration by weight between 0.05%and 0.12%, tin, having a concentration by weight less than 3%, aluminum,having a concentration by weight between 0.002% and 0.04% and barium,characterized in that the concentration by weight of barium is in therange of 0.0015% to 0.02%.
 2. Lead alloy according to claim 1, whereinthe relative concentration by weight of tin is less than 0.75% and therelative concentration by weight of barium is between 0.0015% and0.015%, so as to obtain a rapidly hardening alloy intended for negativegrids.
 3. Lead alloy according to claim 1, wherein the relativeconcentration by weight of tin is between 0.75% and 1.5% and therelative concentration by weight of barium is between 0.0015% and 0.02%,this alloy being intended for positive grids.
 4. Lead alloy according toclaim 3, wherein the relative concentration by weight of calcium isbetween 0.06% and 0.085% and the relative concentration by weight of tinis between 0.9% and 1.4%.
 5. Lead alloy according to any one of claims 1to 4, further comprising bismuth with a relative concentration by weightof between 0.001% and 0.025%.
 6. Lead alloy according to claim 1,further comprising silver with a relative concentration by weight ofless than 0.005%.
 7. Lead-acid battery grid, which comprises a part madeof a lead alloy according to claim
 1. 8. Lead-acid battery,characterized in that it comprises at least one grid according to claim7.
 9. Lead alloy according to claim 1, further comprising silver with arelative concentration by weight in the range of 0.0005% to 0.005%. 10.Lead alloy according to claim 2, further comprising silver with arelative concentration by weight of less than 0.005%.
 11. Lead alloyaccording to claim 3, further comprising silver with a relativeconcentration by weight in the range of 0.0005% to 0.005%.
 12. Leadalloy according to claim 4, further comprising silver with a relativeconcentration by weight in the range of 0.0005% to 0.005%.
 13. Leadalloy according to claim 5, further comprising silver with a relativeconcentration by weight in the range of 0.0005% to 0.005%.
 14. Lead-acidbattery grid, which comprises a part made of a lead alloy according toclaim
 1. 15. Lead-acid battery grid, which comprises a part made of alead alloy according to claim
 2. 16. Lead-acid battery grid, whichcomprises a part made of a lead alloy according to claim
 3. 17.Lead-acid battery grid, which comprises a part made of a lead alloyaccording to claim
 4. 18. Lead-acid battery grid, which comprises a partmade of a lead alloy according to claim
 5. 19. Lead-acid battery grid,which comprises a part made of a lead alloy according to claim
 6. 20.Lead-acid battery grid, which comprises a part made of a lead alloyaccording to claim
 7. 21. Lead-acid battery grid, which comprises a partmade of a lead alloy according to claim 8.